Different methods and devices are known for counting microorganism colonies grown in, for example, petri dishes. Manual counting of colonies by trained laboratory personnel is well known. That method has many disadvantages including the cost associated with the use of skilled technicians to perform the time-consuming chore of manual counting, as well as the limited accuracy in the counts achieved.
Those problems are further compounded when early detection of microorganism colonies in cultured petri dishes is required. Early detection is very useful for manufacturers because it allows the manufacturer to cease production of what would likely be scrap or waste products, also avoiding further processing of those contaminated products which would result in additional expenses.
One example of a beneficial application of early detection is in testing for microorganisms in food products. Samples of the products are taken and culturing devices are inoculated and incubated for a period of 24 or more hours to obtain counts of microorganism colonies indicating the level of contamination in the product. If the samples indicate excessive contamination, the product must often be discarded. Reliable early detection and quantification of excessive contamination in the range of 6 to 12 hours after inoculation would be welcomed by manufacturers because it would allow them to identify contaminated products early in processing, thereby avoiding additional expenses incurred in processing product that will be discarded and possibly contaminating additional product by running it through contaminated processing equipment.
Although technicians can perform early detection of excessive contamination using culturing devices, there are disadvantages associated with having technicians provide the counting as opposed to automated detection systems.
An important indicator of early colony growth is the rate of growth or change between successive readings of the culturing devices. It is difficult, if not impossible, for a human technician to accurately gauge the rate of growth or to distinguish the minute changes in growth indicia for what could be hundreds of culturing devices, all of which would be monitored by a single technician. It is also typically more expensive to employ technicians to provide colony counts and, given the additional difficulties associated with early detection, those costs could be expected to be even higher still.
Automated systems for counting microorganism colonies are known but are typically directed at producing total counts of fully incubated growth media, i.e., growth media that have been incubated for 24 hours or more. The known systems can be separated into two basic categories.
The first category includes systems employing cameras or video equipment in conjunction with hard wired circuits or digital computers to count the number of colonies in a culturing device or detect overall contamination levels in culturing devices by measuring total light absorption of the culturing devices. Examples of such systems are described in EP Publication No. 0 301 600; U.S. Pat. No. 3,811,036 to Perry; U.S. Pat. No. 5,003,611 to Miyake et al.. and French Publication No. 2 602 074.
Those systems are designed to count colonies in culturing devices which have been incubated for a longer period of time such as 24 or more hours as discussed above. The systems are not designed to provide reliable early counts of the colonies on a culturing device.
The second category of automated counting systems typically uses an array of photodetectors and hard wired circuitry to perform the counting process. These systems typically provide signals which indicate that a colony is either existing or not existing. They do not supply information regarding the intensity of the colonies or their rate of growth between intervals. Because the systems are unable to provide indications of the varying intensifies of the indicators used to determine colony growth, they are not particularly useful for the early detection and counting of microorganism colonies.
Because the known automated counting systems are designed to count colonies on a fully incubated culturing device, detect overall contamination levels in culturing devices by measuring total light absorption of the culturing devices or merely count colonies without measuring the intensity of the indicia of colony growth, no automated method for producing a reliably accurate early count of microorganism colonies is known.
Reliable early detection and counting, however, can be accomplished by monitoring minute changes in one or more specified indicia of colony growth. Such indicia can include indicators which are not visible such as the acid or enzymes produced by microorganism colonies during growth and other indicia which may or may not be visible to the naked eye.
As a result, a need exists for a method of providing early detection and quantification of microorganism colonies in inoculated culturing devices by detecting early changes in specified indicia of colony growth.